| Mass-selected and bulk faba bean populations, at three developmental stages, were evaluated for the following components of rate-reducing resistance, to two races of Uromyces viciae-fabae, in both field and growth cabinet studies: fleck number (FKN), uredinia number (UDN), infection type (IT), range of infection types (ITR), latent period (LP and LP$sb{50}$), and LPSM, a standardized disease index combining latent period and uredinial density data. In addition, population performance in the field was compared using the following indicators: mean and final rust severity, individual weekly assessments of rust severity, apparent infection rate, and area under the disease progress curve (AUDPC). Significant differences (p-value = 0.01) among the populations were found for all resistance components and performance indicators. There was some variation in the expression of these characters among individual faba bean populations, but the division between the mass-selected and bulk populations was distinct. The mass-selected populations had fewer flecks and uredinia, a smaller infection type, a narrower range of infection types, and a longer latent period, in addition to reduced rust development in the field as determined by the performance indicators. The developmental stage of the faba bean plants, at the time of inoculation, significantly affected all of the components in the growth cabinet experiments and most in the field studies, suggesting that selection for rate-reducing resistance necessitates the use of plants at the same developmental stage. When plants were inoculated with the rust races individually, a significant race effect was observed for all of the components examined in the growth cabinet experiments and for FKN, IT, ITR, and LPSM in the field. Differences were significant between the two test years for all of the components and performance indicators. Comparisons between components evaluated in the field and those evaluated in growth cabinets indicated that the components UDN and latent period, and the index LPSM corresponded best with population performance in the field. These components could effectively be used to screen faba beans in growth cabinets for rate-reducing resistance. On the other hand, the components FKN and IT did not correlate well with the field results. |
